In psoriasis the skin becomes inflamed and red eruptions appear on the surface of the skin that begin to itch excessively. These areas form thickened areas (plaques) that are covered with silvery scales over the reddened lesions. The skin at the joints may crack. Location: Psoriasis most often occurs on the elbows, knees, scalp, lower back, palms, and soles of the feet. However, no area of the skin is exempt, including the genital area. The disease may also affect the fingernails and toenails, and the soft tissues inside themouth. About 15 percent of people with psoriasis  have joint

inflammation that produces arthritis symptoms.This condition is called psoriatic arthritis. Psoriasis is categorized as mild, moderate, or severe, depending on the percentage of body surface involved and the impact on the patient's quality of life.

Course of diseases:
The course of psoriasis is characterized by remissions and relapse. At some instances the patches disappear, just to appear after some period of time.
There are various factors ranging from climate, stress, infections and injuries that can trigger flare up of disease within short span of time even within few days. On the other hand there are certain other factors such as sunlight that significantly reduces the intensity of problem.

Impact on health:
In some cases, psoriasis is so mild that it may go unnoticed. At the opposite extreme, there are victims having psoriatic patches almost everywhere on the body. People with psoriasis may suffer discomfort, including pain and itching, restricted motion in their joints, and emotional distress.
The unpleasant appearance of the patches, the chronic itching and flaking of psoriasis although is not life threatening, has definite impact on the self-esteem and life style of the psoriasis victim. Substantial time and money are spent trying to keep it under control.

Incidence:
Psoriasis affects between 1-2 percent of general population. In US alone there are about 5.5 to 6 million people suffering from psoriasis.
Both males and females get psoriasis in equal numbers. It can strike at any age, but most often in adults between 15 and 35 years. However, a first-time diagnosis of psoriasis has been seen in very old people, and in newborn babies and small children.

Pathology:
Psoriasis is a chronic (long-lasting) skin disease characterized by scaling and inflammation.
Our skin is mainly made up of two layers: epidermis (outer layer) and dermis (inner layer). The cells of epidermis are borne in dermis and then they move up. At a regular interval of 28-30 days, the cells of epidermis are replaced by new cells formed in dermis.

In psoriasis, this process of cell production in dermis is sped up. New cells are formed and moved upward to the skin surface faster than they can be incorporated into skin. The excess cells accumulate and are scaled off in the form of flakes.
Psoriatic plaque has other features also, including inflammatory cells and dilated small blood vessels that contribute to both the appearance and the symptoms of a psoriatic lesion.